"lispier" regexps, l*last-child stuff

Probably against best practices to commit monolithic patches, but this
is still an unreleased library, so I don't care.

Not really sure I care for the sexp-based regexps, but they do make it
easy to use the same regexp bits across several places, and I don't
have a lexer/parser handy, so they'll have to do for now.